He has also worked with Joan Armatrading, Paul Young, The Rutles, Art Garfunkel, Kiki Dee, Mastermind, John Coghlan's Diesel Band, Elkie Brooks, Judie Tzuke, Imagination, Bucks Fizz, Jennifer Rush and The Bonzo Dog Doo-Dah Band, among others.

He left in 1992, but later returned for the tour promoting Sunsets on Empire (1997) and co-wrote two and performed on three tracks on Raingods with Zippos (1999).

Simmonds had a long-standing relationship with Neil Innes, hence The Rutles (including all the arrangements on Archaeology 1996) and The Bonzo Dog Doo-Dah Band, whose studio album Pour l'Amour des Chiens was co-produced by Simmonds & Innes.

Simmonds worked with the French band from Bordeaux XII Alfonso on The Lost Frontier (1996), Odyssées (1999), Claude Monet vol.2 1889–1904 (2005), Charles Darwin (Fall 2011).

As influences, he cites progressive rock acts such as early Genesis, Emerson, Lake & Palmer and Pink Floyd.